Process for cutting helical gear-wheels.



- W. P. ZIMMBRVMANIN. PROCESS FOB. CUTTING HEL-IGAL GEAR WHEELS.

.arrmonfron FILED' Dnc. 29,;1911.

-. menge@ Sept. 3, 411512.

Hanns-snuff V1.

UNITED STATES PATENT oEEIcE.

WILLIAM F. ZIMMERMANN, OF NEWARK, NEW JERSEY, ASSIGNOR T0 GOULD & EBERF HARDT, OF NEWARK, NEW JERSEY, A CORPORATION OF NEW JERSEY. i

l rRocEss Foa CUTTING,l HELrcAL GEAR-WHEELS.

Specification of L'etters Patent.

Application led December 29, 1911. Serial No. 668,439.

To all whom t may'ooncem.'

'Be it known that I, WILLIAM F. ZIMMER- MANN, a citizen of the United States, and aresident of Newark, in the county of EsseX vand State of New J ersey,'have invented certain new and vuseful Improvements in Processes for Cutting Helical .Gear-Vheels, and do hereby .declare the'followingf specification, .taken in connection with the drawings forming part of thesame, to be a full, clear, concise, and exact description of the invention andthe best'mode contemplated to apply said principle, so as to distinguish lit from other inventions and to enable any person skilled `in the art to which it appertains or with which it is most nearly connected to make, construct, and use-the same.

This' invention relates primarily to' a l method of generating the teeth in helical gear wheels by means of a helical or hob cutter, and employing apparatus similar to that shown and described in'the co-pending ap.

plication No. 657,970, led November 1,1911,

i a processof cutting helical gear wheels with by tl'reapplicant.

The'objectof -thisinvention is to provide -'a helicalfcutter, by imparting a single continuous-,'and'u1ibroken motion between the cutter and the work blankin a ratio that is dependent upon theV number of 'teeth to be cut and a lixed constant, which constant is determined bythe linear pitch of the gear d the-*approximate feed desired, and of 'arting a feeding motion to said cutter blank -spindle relative'to each other, `el-fwitbl the axis ofsaid spindle, lwhich i offthegear and said lixedconstant.

' The-advantage of this invention resides 401 1 ables more accurate gears to be readily pro- `duced than bythe process described in lthe above co-pending application. This ad-- in'the practising of the process which envantage results. from the arranging of the change gears between th'e cutter and the work blank according to a fixed constant, to thereby establish an absolutely correct ratio betweenthe cutter and the work blank, .for

the 'given variables, anu the error, ifany,

will then be only present between the Aworkblank and t-he rfeeding motion of said cutter.v .In the co-pending application, the feeding motion relative to the rotations of the blank i spindle was absolutely exact, and the error was allowedto cumulatein the change gear ratio between the cutter and the work blank.

ing motion is dependent upon the linear The objection to this method of cutting helical gear `wheels is that when the error is so located, that is, between the cutter and the work blank, it is cumulative, and it requires va very high degree of accuracy in selecting -the feed to the cutter. 'By thus allowing the error to. cumulate betweenthe work blank and the lfeed to the cut-ter, t he Same' does not .attain the .propor'tions as would-bathe case ed was'absolutely exact because when the Patented Sept. 3, 1912.-`

the factor for the number of teeth to be cut A is entirely eliminated. l

By the process described in theco-pending-application, the limits allowed for inaccuracy. infthe gearing ratio between thegcut- `ter and the work blank, as found bythe proof formula therein shown`were between 1.015 and .985,.whereas with the process described in this invention the allowable limit oferror was set between 1.001 and 999;and it is possible to obtain a gearing ratioybetween the latter limits by the process of., this invention :with less diiculty than her'tofore by any previous process;

This process has enabled Before describing theapparatus to prac- Thcamount of calculation hereinthe calculatms for the gear ratios to be simplified to'such a tise the invention, the 'necessary formulae will be derived after the4 followingnotation and general formulae:A

PNCznormal clrcular pitch ofhelical gear to be cut or the shortest distance between `60 after described, th'e-formula for the number L=lead of the, helices or. the advance in one turn. ,Y y

Thej follow-ing formulae are ordinarily used to determine the various parts of a helical gear when the -usual lmown quantit-iesare given, to Wit: PNC, N and X.

sin X tan. :z: -PNC sin. X

In cutting a `helical gear upon any automatic helical gear cutting machinfewith a helical cutter, it is always necessary to rotate the blank in unison with the helical cutter at a speed depending upon the n um` ber of teeth to be cut, while at the same time,

the cutter is advanced across the face of the blank in what results in a helical path upon the peripheral face of the blank, passing around the axis ofthe blank, such path being due in other machines to differential gearsinserted in the cutter drive or indexing mechanism. This invention produces a helical path by imparting rotary motionto theblank'and cutter, in accordance with the number of` teeth to. be cut and a ixedconstant, which constant is dependent upon the linear vpitch of the gear to be-cut and feed desired. The Afeeding motion is par, allel to the aXis of the gear blank and can vbe relative to either` the rotations of the cutter or the g'ear blank." In this invention-th feedl is preferably arranged relativeto th rotations of the gear blank,` and the formulae hereinafter derived are particularly adapted thereto.

To index in a machineas will be hereinof teeth would' be gq Where K represents a constant depending upon the relative ratios of rotation of the work spindle to that of the helical cutter, and N represents the number of teeth to be cut. y

The formulae used in the present invention are obtained by the following derivation:

Let T equal the fixed constant derived by dividing the linear .pitch PL by the required feed F. Then o u PNC PL rn-rn. air e And let equal the ratio required to cutspur gears, then by adding or' subtracting f .l from N, we obtain K N :F T which is Athe formulato establish the xed ratio between the cutter and the work blank. The formula for the. feed gears would be derived by multiplying the required feed F by a constant If-r which equals KF andin which K is a constant determined from the relative ratios of the constant gearing between the work blank and feed screw. This formula is expressed and used in terms of the fixed constant T and is derived as Substituting the valueof F in KF We obtain Y KPL KPNC T T sin. X-

To obtain a lproof formula whereby it may be ascertained whether the gears selected according to formula II will be With- 1n the limits herein before described, it is onl'y necessary to divide the formula II by the gearing ratio used, thus'letting R equal the ratio of gears used then KPNC KPN T sin. X RT sin. X

` The 'digit l resulting from the proof formula expresses the extra rotation or the approximation required for the lead of the helical gear. I

. In practising this invention a chart is compiled containing the fixed constants T for the Various conditions met with in ordinary practice. It then only becomes necessary to consult the table of factors T and substitute the other known quantities to find the gearing ratio. Furthermore this processhas enabled the gearing ratios, as expressed by formulae I and II, for 'the numerous conditions, to be readily put in chart out the expenditure of months, if not years .of labor and atconsiderable expense.

The annexed drawings and description set 'forth in detail certain contrivances embodying means constituting, however, but one of the' various mechanical forms in which the principle of the invention may be used.

The novelty of the invention will be readily understood from the drawings, which show a construction for practising the invention in its prefer-red form, and Ifrom the following description thereof, and is more particularly pointed out and distinctly claimed in the claims ,annexed to said description. f

In the drawings :l lFigure 1 is a side view of an apparat-us embodying' t-he vfeatures necessary to produce helical gear wheels with a helical cutter in accordance with this Fig. '2 is a sectional plan View ter and Work blank. Fig. 3 is a partial rear eleva-tion in section to exhibit the driving mechanism.

Proceeding now with the detailed description of the mechanism to practise the invention, the main frame I is provided with. a stanchion 2 at one-endv thereof, preferably cast integral therewith. A work slide 3 is adjustably mounted 'on the horizontal portion of t-he main frame I and is provided with a revoliible work s indle 4 therein, in Which-the work arbor 5 1s secured, whereby the gear blank 6 may-be centered andsecured to the spindle 4 inthe usual way. A

worm or index wheel 7 is securedto the lower end Vof the work spindle 4 andis ro- Atated. by the worm 8 in engagement therewith. The indexing worm 8 is mounted in bearings 9 of the work slide 3 and is provided with a gear 10 secured to one end thereof, to engagewith `the gear 11 which is 1 `slidably keyed to the index shaft 12. The

index shaft 12 extends along the side of the main frame and is mounted in bearings at either end thereof and connected to the indexing drive shaft 13, by means of a compound train of change wheels which are arranged in accordance with the formula here- Y inbcfore described.

also rotatably mounted on the stud 16, is'

arranged to rotate in unison with said secondv change gear 15 and meshes with the change gear 19 securedto, and rotatable with the index shaft 13.. The stud 16 is slidably arranged in the arm 17 to accommodate the various diameter change gears,

and is secured to said arm by a bolt 2O.- The arin 17 carrying the stud 16 is pivotally mounted upon'the index shaft' 12 and is secured 1n the various positions to the indexing shaft bearing 21 by 'means of 'the bolts 22. The index shaft 13 has secured thereto .and rotatable therewith, a, feed driving gear 23 which meshes with a gear 24 secured to the feed drive shaft 25. A change gear 26, is secured to the other end of said feed drive shaft 25 and engages with the change gear 27, rotatably mounted on the stud 28. The change gear 29, also rotatably mounted on said lstud 28, is arranged to rot-ate the change gear 3() secured to the worm shaft 31, to drive the feed to the helical cutter as hereinafter described. The stud 28 is slidably arranged in the arm 32to accommodate the Various diameter change gears and is pivot-v ally mounted upon the feed worm shaft 31. Said arm 32 can be secured to the frame in any of its pivotal positions by the bolt 33.

i The index shaft 12 which imparts motion directlyto the gear blank receives it-s niotion, from the mainfshaft 34, through hthe worm wheel 35 secured to the index drive shaft 13 and rotated by the worm 36 secured to and rotatable vwith said main shaft 3 4. rIhe ratio of the worm wheel 32 and the worm 36 must be equal to or a factor of the ratio between the' main driveshaft 34 and the helical cutter, preferably the former, so that for each rota-tion' of the cutter, the index drive shaft 13 will make a complete rotation or a multiple thereof. Any other' relations may, however, be established between the cutter and the work blank so as to result in some convenient factor which can be used in the formula without difficulty in factoring.

The main drive shaft 34 is rotated by the cone pulley 37 which is mounted on the hub 38 of the mainframe I. The helical cutter 39 is secured in any suitable manner to the cutter shaft 40 mounted to rotate in thev swivel carriage '41. The carriage \42 on which the swivel carriage 41 is mounted, is vertically adjustable on the sanchicn 2. parallel to theaxis of the gear blank. The swivel carriage-41. is scoured to the cutter carriage 42 in any angular position in rela-- tion to the gear blank, by means of bolts LT-l.

,the heads of which are'in engagement with the circular T slot 44, arranged in said cutter carriage 42. The cutter shaft has secured thereto, and rotatabletherewith, -t

drive gear 45, meshing with the pinion 46,

which is secured to the shaft 48, also rotatably mounted in the swivel carriage 4l. On the other 'end of the pinion shaft 48, a bevel gear 49 is securcd,.engaging with n bevel gear 50, which is secured to the center shaft 51, about which the swivel carriage 41 pivots. By pivoting the helical cutter about the center shaft 5l, a rotatable connection through the bevel gears 50 and 49 is insured in any angular position of the cutter." -'A bevel gear 52 is secured to the 'other end of the shaft 51, and meshes With the bevel gear 53', Which is rotatably mount-` ed in the .cutter carriage-and is slidabl keyed to rotate With the vertical cutter sha t 54.' The cutter drive shaft 54 is mounted in bearings provided in thestanchion 2'. A

i bevel` gear 35 is secured to the lower end of said cutter drive shaft 54 and engages with a bevel gear 56-Which is secured to and rotatable v'ith the main shaft 34. Thevfeed of the cutter parallel .to the axis of the gear blank is obtained from the index shaft 12 through the gears 23 and 24, and change gears 26, 27, 29 and BO'as hereinbefore described. From this connection it is obvil ous that the feeding motion of the cutter is dependent upon and-relative to the. rota- .t-ions of the blank spindle. The feed Worm s haft 31 is provided with a fcedvvvorm 5 7 preferably integral therewith, Whichiengages With the feed Worm Wheel 58, secured 'to the cutter feed screw 59. '59 is mounted in bearings of the main frame Said feed 'screu7 and engages a threadedportion 60 of the cutter ca1riage-42-and is rotated through the Worm and Worm Wheel 57 and 58 and change gear connections hereinbefore dcscribed.

From the construction' as described it.Will

' .be seen that rotary motion is transmitted directly from the main shaft to the gear blank and from Athe main shaft to the cut ter,'but it is not'necessary that the cutter and the Work-blank be independent branches from the samesource of motion. It is merely essential for. this invention that there be a continuous and unbroken line of motion The feeding motion is obtained from the inbetween the cutter and the Work blank.

dex shaft Which' rotates in synchronism with the blank spindle, and the 'feeding motion of the cutter is therefore controlled and dependent upon the rotations of the blank spindle. Compound feed change gears have been introduced in the feed train to facilitate the arranging of the feed change gears.

Having described'my invention, l claim aud desire to secure by Letters Patent:

l. The process for cutting the teeth of l. helical gear Wheels, that have a directrix coinciding vvith. the' gear. blank axis, consisting of rotating a helicalv cutter, andimparting rotary motion lto 'a gear blank relative to said cutter through a single continuous unvarying motion froml a driver to'saidcutter and gear blank,`respec tively, therelative rotations of the cutter and gear blank being dependent upon the number of teeth-to be cut 'in the gear blank, and a constant'de- 'rived as described, and of feeding said cutter relative to the rotations and parallel with the-axis of said gear blank inr a ratio dcpendent -upon the linear bitch of; the gear blank andsaid constant.

2. The process for cutting the teeth ot helical gear Wheels that have a 'directrix coinciding with the gear blank axis, consisting of imparting a single continuous and unvarying rotary motion between a helical cutter and gear blank from a driver tosaid vcutter and gear blank, respectively, in

a ratio dependent upon the number of coinciding With the gear blank axis, consist ing of imparting a single continuous and un- 'varying rotary motion between a helical cut-` ter 'and gear blank from .a driver to said cut ter Aand gear blank, respectively, in a ratio .dependent upon the number ofteethto be 'cut in the blank, minus the reciprocal of a fixed const-ant, and of feeding saidcutter relative to said single continuous and. un-

varying rotary motion in a ratio dependent upon the linear pitch of the gear blank divided by said fixed constant.

4. The process for cutting the teeth of helical gear Wheels that have a directrix coinciding With the gear blank axis, consisting of rotating a helical cutter, and imparting rotaryinotion to a gear blank rela` tive to said cutter through a single continu ous unvarying motion from a driver to said.

blank and cutter, respectively, said relativel rotations being dependent upon the ratio of the intermediate gearing multiplied by a fixed constant and the product divided by the product of the numberof teeth to be cut by said constant,A minus one, and of feeding said cutter relative to the rotations and parallel tothe axis of. said gear blank in a ratiodcpendent upon the ratio of tl e intermediate gearing multiplied by the normal circular pitch of the gear, and the product divided by said fixed constant multi- .plied bythe sine of the angle of the helical teeth tb beproduced.

WILLIAM F. ZIMMERMANN. v

lVitnesses H. W. JAooBsoN, B.' E. BARNES. 

